Energy applicators adapted to dielectric heating

ABSTRACT

A dielectric heating system with which the power density applied to the product being treated can be at least doubled without risk of electric arcs. This invention is particularly suitable for treatment of compounds that absorb electromagnetic waves weakly (low dielectric constants). In particular, fatty substances such as oils, butters, waxes and fats can be treated (refining, hydrolysis, transesterification, interesterification, etc.), derivatives thereof (esterification, polymerization, alcoholysis, ethoxylation, hydrogenation, etc.) under static or dynamic conditions, as can hydrocarbons and aromatic compounds. This system can also be used advantageously for polar or polarized compounds, because the power absorbed is increased very significantly, with large production gains. In particular, fatty or non-fatty alcohols (oleic alcohol, glycol, glycerol, mannitol, sorbitol, polyglycerols, vitamins, etc.), carboxylic acids, amines and similar compounds can be treated under static or dynamic conditions.

TECHNICAL FIELD OF THE INVENTION AND PROBLEM POSED

The present invention relates to the design and use of energyapplicators, and more particularly to resonant cavities and chimneymembers of shapes and dimensions adapted to the dielectric heating ofany compound, regardless of the dielectric constants thereof.

The usual microwave and high-frequency applicators are equipped withtraditional chimney members that make it impossible to work at highpower density without the risk of electric arcs. The purpose of thechimney members used by the person skilled in the art is aimed atsubjecting a product (liquid, solid, gaseous or a mixture of the threestates) to electromagnetic waves under static or dynamic conditions,while preventing waves from leaking out of the waveguide. The chimneymembers, of traditional shape, preferably of cylindrical shape, make itimpossible to reach the desired temperature level rapidly and/or totreat a larger quantity of product without the risk of electric arcs. Incontrast to polar or polarized molecules, for which energy transfer isoptimum, a high power density proves to be necessary to achieve heatingof compounds, characterized by low dielectric constants, that absorbelectromagnetic waves weakly.

Thus there exists a serious technical problem, posed by the risks of“discharge” or electric arcs and the industrial consequences thereof,which problem represents a major concern in industry, because of theimportance of the industrial applications indicated here. By virtue ofthe invention, the time for processing the products can be very greatlyshortened and, in parallel, the industrial efficiency can be improved.

SUMMARY OF THE INVENTION

After numerous attempts, the Applicant has discovered a new shape orgeometry for the chimney member, in particular a chimney member ofconical shape or geometry, that makes it possible to heat any type ofproduct at microwave frequencies or high frequencies under static ordynamic conditions with a high power density without risk of electricarcs or “discharge”.

APPLICATIONS

The invention makes it possible to achieve heat treatments of compoundsthat absorb electromagnetic waves weakly in a manner that is just asefficient and rapid as for polar or polarized compounds. The time andenergy savings, combined with a lower investment cost, make it possibleto ensure that the applications with dielectric heating are faster andmore economical.

The invention relates in particular, but non-limitatively, to thetreatment of fatty acid esters (unsaturated or otherwise), ofhydrocarbons (unsaturated or otherwise), of aromatic compounds and ofderivatives of the latter. It is also of great interest, however, forproducts that strongly absorb electromagnetic waves, because it makes itpossible to increase the production capacity of a given system (fattyand non-fatty alcohols, carboxylic acids, amines, etc.).

The present invention relates to all the heating applications involvinga single reactant or a mixture of reactants in variable proportions,with or without catalysts, with or without process or “working” gas.Non-limitative examples of heating applications include esterification,transesterification, epoxidation, sulfatization, phosphatization,hydrogenation, peroxidation, isomerization, dehydration, quaternization,amidification, polymerization and polycondensation reactions as well asall the usual treatments such as decolorization, deodorization and theother systems for elimination of volatile compounds.

In fact, the invention is applicable quite particularly to all reactionsof “lipochemistry”, and notably has a very strong interest for the caseof products that absorb electromagnetic waves weakly.

This innovative technique makes it possible, for example, to synthesizepolymers of unsaturated fatty acids, of esters of unsaturated fattyacids, of unsaturated hydrocarbons or of derivatives of such products bymeans of dielectric heating with microwaves. On this subject theApplicant has filed French Patent Application 98-13770 and PCT PatentApplication WO 00/26265 (PCT/FR99/02646).

PRIOR ART

The technical field of the present invention relates to the use ofmicrowave or high-frequency electromagnetic waves both for heatingapplications on compounds that absorb radiation weakly and on compoundswith high dielectric constants.

The microwave (MW) frequencies range between about 300 MHz and about 30GHz, preferably 915 MHz (authorized frequency with a tolerance of 1.4%)or 2.45 GHz (authorized frequency with a tolerance of 2%).

The high frequencies (HF) range between about 3 MHz and about 300 MHz,preferably 13.56 MHz (authorized frequency with a tolerance of 0.05%) or27.12 MHz (authorized frequency with a tolerance of 0.6%).

The power (in watts) absorbed by a material under HF or MW treatment isgiven by the following formula:Pa=kfε″E²VWith:

Pa: power absorbed in W.

E: electric field created in the material in V/cm.

f: frequency of the waves.

K: constant (M.K.S.A)=5.56.10⁻¹³

V: volume of the material in cm³.

ε″: material loss factor=ε′ tan δ

ε′: real relative permittivity of the material=ε₀*ε_(R)

ε₀: permittivity of vacuum

ε_(R): dielectric constant

tan δ: loss angle

ε′ represents the tendency of a material to become oriented in the field

and tan δ represents its capacity to dissipate heat.

Remark: for air or vacuum, ε′=1 (which is the lowest value for ε′) andtan δ=0, meaning that ε″=0.

Let us consider a system comprising a guide designed to carry wavescorresponding to a given frequency. The product to be heated is placedin a reactor of material that does not absorb the waves (Pyrex, quartz,etc.). This reactor is positioned inside the applicator formed fromsingle-mode cavities that resonate at the emission frequency along abeam in the direction of the waveguide. The microwave applicator isequipped with chimney members, traditionally cylindrical to conform tothe shape of the reactor being used (see FIGS. 1, 2, 3). The purpose ofthese chimney members is to prevent waves from leaking out of thewaveguide. The discharge phenomenon occurs in zones where the tubecontaining the product to be treated develops disruptive voltages, or inother words where the accumulated energy is such that ionization of themedium (electric spark) occurs. The electric field is characterized bythe ratio of the voltage between two points to the distance separatingthese two points. The risks of discharge occur in the zones where thefield is too concentrated.

The reactor can traverse the waveguide at right angles to the directionof propagation of the waves or else parallel to the direction of thewaves (see FIGS. 2 and 12). The person skilled in the art willunderstand that these two positions are not the only possibleconfigurations and that the invention encompasses all other intermediatepositions.

Reactants:

For the present invention, the reactant or reactants can be chosen fromamong the products that absorb electromagnetic waves weakly or theproducts that absorb strongly or a mixture of the two, with or withoutadditions of one or more catalysts or weakly or strongly absorbingadditives and/or of process gas.

Among the strongly absorbing products there will be understood fatty ornon-fatty alcohols, fatty or non-fatty amines, carboxylic acids,acetals, ketones, enols, peracids, epoxides and, more generally,chemical compounds containing a polar or polarized function, especially

-   -   as alcohols: sorbitol, glycerol, mannitol, glycols, vitamins        (such as tocopherol, ascorbic acid, retinol), polyphenols,        sterols (including the phytosterols) and analogous compounds,        and,    -   as amines: ammonia, primary, secondary and tertiary alkylamines        (such as methylamine, dimethylamine, trimethylamine,        diethylamine), fatty amines (such as oleic amines, alkylamines        of coconut oil), aminoalcohols (such as monoethanolamine MEA,        diethanolamine DEA, triethanolamine TEA;        3-amino-1,2-propanediol, 1-amino-2-propanol) and ethoxylated        amines (2,2′-aminoethoxyethanol; amino-1-methoxy-3-propane).

All of these amines may be saturated or unsaturated, straight-chain orbranched.

Among the catalysts or additives there will be understood, asnon-limitative examples, the usual acid catalysts (paratoluenesulfonicacid, sulfuric acid, phosphoric acid, perchloric acid, etc.), the usualbasic catalysts (sodium hydroxide, potassium hydroxide, alkali metal andalkaline earth alcoholates, sodium acetate, triethylamines, pyridinederivatives, etc.), the acid and/or basic resins of the Amberlite™,Amberlyst™, Purolite™, Dowex™ and Lewatit™ type, zeolites, enzymes,carbon blacks and activated carbon fibers.

Among the weakly absorbing products there will be understood the animalor vegetable oils and fats and the polyterpenes, some of which arederived from the said oils and fats.

Oils or Fats of Animal Origin

As oils or fats of animal origin there can be cited, among others, spermoil, dolphin oil, whale oil, seal oil, sardine oil, herring oil, sharkoil, cod-liver oil, neatsfoot oil and beef, pork, horsemeat and muttonfats (suets).

Oils of Vegetable Origin

As oils of vegetable origin there can be mentioned, among others,rapeseed oil, sunflower-seed oil, peanut oil, olive oil, walnut oil,corn oil, soybean oil, linseed oil, safflower-seed oil, apricot-kerneloil, sweet-almond oil, hemp oil, grape-seed oil, coconut oil, palm oil,cottonseed oil, babassu oil, jojoba oil, sesame oil, argan oil,milk-thistle oil, pumpkin-seed oil, raspberry oil, Karanja oil, Neemoil, poppy-seed oil, Brazil-nut oil, castor oil, dehydrated castor oil,hazelnut oil, wheat-germ oil, borage oil, onager oil, Tung oil and talloil.

Components of Animal or Vegetable Oils

It is also possible to use components of animal or vegetable oils, suchas squalene, which is extracted from the unsaponifiable fractions ofvegetable oils (olive oil, peanut oil, rapeseed oil, corn-germ oil,cottonseed oil, linseed oil, wheat-germ oil, rice-bran oil) or containedin large quantity in shark oil.

These oils and fats of animal or vegetable origin as well as thederivatives thereof can be subjected to a preliminary treatment aimed atmaking them more reactive or, on the other hand, less reactive. Theinvention relates both to an isolated reactant and to a reaction mixturecontaining two or more components. These reaction mixtures may containequivalent proportions of each component, or certain components maypredominate.

Unsaturated Hydrocarbons

As unsaturated hydrocarbons there can be cited, as single substances oras mixtures, and as non-limitative examples, an alkene, such as aterpenoid hydrocarbon or hydrocarbons, meaning a polymer or polymers ofisoprene, or a polymer or polymers of isobutene, styrene, ethylene,butadiene, isoprene or propene, or a copolymer or copolymers of thesealkenes.

Type of Energy Applicator

The choice of energy applicator depends on the technology used(high-frequency or microwave), on the dimensional characteristics of theproduct to be treated and on the method of treatment thereof.

In the case of polar or polarized molecules, for which energy transferis optimum, there exists a certain number of standard applicators thathave proved their effectiveness.

High-frequency applicators include essentially:

-   -   applicators of capacitive type, formed from two capacitor foils        between which there is applied the high-frequency voltage of the        generator. They are used for heat treatment of materials whose        volume comprises a parallelepiped in which one of the sides is        sufficiently thick (>10 mm).    -   rod applicators for flat materials, comprising tubular or rod        electrodes. They are used for heat treatment of materials whose        volume comprises a parallelepiped in which one of the sides is        not sufficiently thick (<10 mm).    -   Applicators for thread-like materials, formed of loops.

For the microwave applicators, there can be cited:

-   -   localized-field applicators: single-mode cavity    -   diffuse-field applicators: multimode cavity    -   near-field applicators: radiating-antenna guide

In the case of weakly absorbing molecules, the choice of applicators ismore complicated. In fact, the applicator must transmit much moreelectromagnetic energy to the product in order to heat it, whileavoiding electric arcs.

Heating at microwave frequencies is preferred to high frequencies, forwhich the risk of discharge is greater. In fact, the loss factor ε″ andthe frequency are lower in this case. For equivalent absorbed power, andin keeping with the formula presented hereinabove, the electric fieldincreases, thus increasing the risk of discharge.

A resonant microwave system is recommended: it may be a localized-fieldor a diffuse-field applicator. Nevertheless, the “single-mode” system(localized field), which is formed from single-mode cavities resonatingat the emission frequency along a beam in the direction of the guide, ispreferred to the multimode” system (diffuse field). The single-modesystem avoids inhomogeneous distribution of the electric field and thepresence of hot spots. Similarly, this type of reactor favors thestability of the exposed products.

The person skilled in the art will understand that dielectric heating ofcompounds that absorb electromagnetic waves weakly is not limited to thesingle-mode microwave system. Nevertheless, this system reduces the riskof electric arcs and permits better control of heat treatments.

The chimney members usually used in the single-mode applicators havestraight cylindrical shape, in order to conform more closely to theshape of the traditionally used reactors (see FIG. 3).

The chimney members are placed on both sides of the waveguide in orderto prevent waves from leaking out in the case of tests under dynamicconditions (see FIG. 2). The length of each chimney member is determinedso as to exclude any leakage of waves and to comply with the safetymeasures relating to personnel and telecommunications. The Frenchstandards are currently identical to the British, German and U.S.standards. These standards are generally less stringent for HF than forMW applications: 10 mW/cm² and 5 mW/cm² at 1 inch from the equipment.For the usual cylindrical chimney members, the height is related to thematerial permittivity and reactor diameter by empirical relationships.

For reasons of simplicity and better control of the resonant cavity, thechimney members placed on both sides of the waveguide have identicalshape.

The present invention shows that the single-mode applicator equippedwith the standard cylindrical chimney members, the most suitable of allstandard applicators for weakly absorbing molecules, makes it impossibleto work with high power density without the risk of discharge.

An intricate means of alleviating the problems related to weaklyabsorbing compounds would be to introduce polar compounds such as waterinto the reaction medium, to act as energy-transfer agent and thus toreduce the necessary power density. This alternative is notsatisfactory, however, inasmuch as undesired secondary reactions mayoccur, and additional treatments such as neutralization, washing, dryingor filtration may be necessary to purify the product at the end ofreaction.

One alternative for alleviating the problems related to weakly absorbingcompounds is to remove the static electricity as soon as it develops onthe outside wall of the reactor. For a product that absorbselectromagnetic waves weakly and for a given incident power Pi, theabsorbed power Pa decreases and the losses increase, especially thosedue to static electricity.

In fact:Pi=Pa+lossesWith:

Pi=incident power in W

Pa=absorbed power in W

Losses=heat losses+static electricity

Static electricity is manifested by ionization of molecules of the air.It accumulates on the nonconductive outside walls of the reactor untilan electric arc develops. To remove the static electricity, it isnecessary either to promote good ventilation by humid air or by anothergas having comparable values of dielectric constants (such as sulfurhexafluoride SF6 at 1 bar) (1^(st) solution), or to adapt the shape ofthe chimney members in such a way that they are open to the air (2^(nd)solution). The first solution does not seem advantageous for reasons ofinstallation complexity, safety and cost.

Thus there exists a large and recognized need to improve the knownenergy applicators, and in particular to adapt them non-limitatively tothe field of the process and reactants of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a microwave device according to oneembodiment of the present invention;

FIG. 2 is a diagram of a microwave applicator equipped with chimneymembers according to one embodiment of the present invention;

FIG. 3 is a cross sectional diagram of a chimney member according to oneembodiment of the present invention;

FIG. 4 is a cross sectional diagram of a chimney member according to oneembodiment of the present invention;

FIG. 5 is a cross sectional diagram of a chimney member and waveguideaccording to one embodiment of the present invention;

FIG. 6 is a cross sectional diagram of a chimney member and waveguideaccording to one embodiment of the present invention;

FIG. 7 is a cross sectional diagram of a chimney member according to oneembodiment of the present invention;

FIG. 8 is a cross sectional diagram of the reactor traversing thewaveguide at right angles in the direction of propagation of the wavesaccording to one embodiment of the present invention;

FIG. 9 shows wavelength characteristics of the configuration depicted inFIG. 8;

FIG. 10 shows a configuration of the chimney member, wave guide andreactor according to one embodiment of the present invention;

FIG. 11 shows a configuration of the chimney member, waveguide, reactorand wave-emitting device according to one embodiment of the presentinvention;

FIG. 12 shows a configuration of the chimney member, waveguide andreactor according to one embodiment of the present invention;

FIG. 13 shows a configuration of the chimney member, waveguide andreactor according to one embodiment of the present invention;

FIG. 14 shows a configuration of the chimney member and waveguideaccording to one embodiment of the present invention; and

FIG. 15 shows a configuration of the chimney member according to oneembodiment of the present invention;

DESCRIPTION OF THE INVENTION

The Applicant has discovered a new shape or geometry for the chimneymember, especially a conical chimney member, which makes it possible toheat any type of product at microwave frequencies or high frequenciesunder static or dynamic conditions at high power density without risk ofelectric arcs or “discharge”.

More generally, the Applicant has discovered that it is desirable toprovide a resonant cavity that extends around the waveguide, fortreatment of the product (in other words to create an “additional”resonant cavity around that present in the waveguide), and in particularto provide one or more chimney members around or on each side of thewaveguide, preferably with identical geometry and adapted so as to forma resonant cavity extending around the waveguide, for treatment of theproduct under consideration.

Thus the invention relates in general to an

-   -   energy applicator, of the type comprising a waveguide and        lateral chimney members, for dielectric heating of any compound,        at microwave frequencies or high frequencies, under static or        dynamic conditions, at relative power density higher than that        of the usual applicators, without risk of electric arcs or        “discharge”, regardless of the dielectric constants of the said        compound, characterized in that the said applicator is provided        with at least one resonant cavity that extends around the        waveguide, for treatment of the product.

More particularly, the invention relates to an

-   -   energy applicator, of the type comprising a waveguide and        lateral chimney members, for dielectric heating of any compound,        at microwave frequencies or high frequencies, under static or        dynamic conditions, at relative power density higher than that        of the usual applicators, without risk of electric arcs or        “discharge”, regardless of the dielectric constants of the said        compound, characterized in that the said applicator is provided        with at least one chimney member of geometry adapted to form a        resonant cavity around the waveguide, for treatment of the        product under consideration,    -   applicator such as described in the foregoing, characterized in        that this cavity is formed on each side of the waveguide,    -   applicator such as described in the foregoing, characterized in        that this cavity is formed around the waveguide by one or more        chimney members,    -   applicator such as described in the foregoing, characterized in        that the chimney member or chimney members is or are placed on        each side of the waveguide, around the resonant cavity,    -   applicator such as described in the foregoing, characterized in        that the chimney members are of identical geometry.

In this context it will be noted that the geometries to be describedreflect the surprising concept that it is possible to work usefully(meaning to treat the product) in a zone larger than that recognizedunanimously in the prior art, or in other words a zone in which theconstant prior art was careful not to work. The discovery of thisprinciple has made it possible on the one hand to create new andoriginal geometries, avoiding discharge, which was the first objective,and on the other hand to obtain, completely unexpectedly, a substantialsavings in treatment time and investment costs. It has been demonstratedin a test that the time for treatment of 60 ml of product in the “zone”or cavity enlarged according to the invention was equal to the treatmenttime necessary for treatment of 33 ml of product in a crucible.

The uniqueness of these new chimney members derives from their shape.They are composed of two main portions: an upper portion, which must beas close as possible to the reactor in order to prevent waves fromleaking out, and a lower portion whose shape flares toward the waveguideso that, according to the invention, electric arcs are reduced and theadditional resonant cavity mentioned hereinabove is created around thewaveguide.

The person skilled in the art will understand that the shape anddimensions of the said additional cavity around the waveguide, or inother words around the resonant cavity normally already present in thewaveguide (which cavity is strictly limited in the prior art), can beentirely varied as a function of the envisioned application and of theapparatus.

In particular, there can be cited the symmetric shapes, and inparticular the shapes composed of at least a conical base, a sphericalshape or a shape of ellipsoidal or analogous volume, the broadestportion opening into the waveguide in all cases.

The upper portion of these new chimney members must be as close aspossible to the reactor in order to prevent leakage of waves. Thisportion may have diverse shapes, such as cylindrical shapes withcircular, rectangular or square cross section, without being limitedthereto. It may also include a plurality of successive different shapes.Nevertheless, the most commonly used shape is the cylindrical shape withcircular cross section, in order to conform best to the shape of thereactor and to avoid the presence of edges, which favor electric arcs.The height of this portion of the chimney member is determined from theviewpoint of excluding any leakage of waves.

The person skilled in the art will understand that this upper portiondoes not necessarily have to be present in the case of completelyshielded systems. In this type of configuration, the problem of wavesleaking out is effectively suppressed, because the entire system thenrepresents a resonant cavity.

The lower portion of these chimney members must be of flared shape, inorder to prevent electric arcs at the waveguide. For this purpose therecan be cited, as non-limitative examples, the conical and/or sphericalshapes having variable angles relative to the vertical, and thepyramidal shapes having square or rectangular bases. As in theforegoing, this portion of the chimney member may have a combination ofthese different shapes. The main parameter that must be taken intoaccount is the base diameter of these flared shapes: it must not exceedthe width of the waveguide. Once the diameter has been chosen, theheight and apex angle of the flared portion are fixed as a function ofthe power used.

In the case of single-mode microwave applicators at 2450 MHz, therecommended waveguide width for remaining in TE 0.1 mode (transverseelectric) ranges between approximately 70 and 100 mm. The TE 0.1fundamental mode of excitation permits the wave to propagate along asingle arc.

At less than 70 mm, the wave does not propagate (cutoff frequency).

At greater than 100 mm, the mode changes to TE 0.2, with two fieldmaxima, implying less homogeneous heating.

The person skilled in the art will understand that the invention is alsoapplicable at other microwave frequencies and high frequencies, and thatsimilar reasoning can be advanced for all of these frequencies.

Although all geometric shapes and combinations thereof can beenvisioned, it is advisable for reasons of simplicity and cost to workpreferably with chimney members of identical shapes and dimensions onboth sides of the waveguide and also with a minimum of combinations foreach.

The invention will be more clearly understood by reading the descriptionto follow and the non-limitative examples below.

In the attached FIGS. 1 to 15, the symbols have the following meanings:

-   MW milliwattmeter-   SR′ cooling system-   I iris (a kind of adjustable diaphragm)-   AP applicator with chimney member or chimney members-   P short-circuit piston-   BC double coupler-   SA automatic stub system (insertable movable screws)-   C safety device (circulator)-   SR cooling systems-   TMO microwave head-   G magnetron generator-   GO waveguide-   R reactor exposed to waves-   CH chimney member or chimney members-   PS upper portion of chimney member-   Pi lower portion of chimney member-   V1, V2, V3, V4 volumes (FIG. 15)

EXAMPLES

The examples below illustrate the interest of the invention as well asof its variants, and will permit the person skilled in the art easily toextrapolate to other dimensions and/or geometries without departing fromthe scope of the invention.

The following examples, which are in no way limitative, illustrate themerit of the invention. They are intended to demonstrate that the usualmicrowave and high-frequency applicators are not adapted to allproducts, and more particularly to weakly absorbing products. To be ableto heat these products without risk of discharge, it is advisable tomodify the shape of the chimney member of these applicators.

The examples also demonstrate the successive difficulties encountered inthe development of the present invention.

I—Appliances Used

The microwave device comprises different elements:

(see FIG. 1)

-   -   The microwave system is composed of a magnetron generator G        operating at the frequency of 2450 MHz (λ=12 cm) at a power        ranging up to 6 kW.    -   The generator transmits the energy to the microwave head TMO,        which will transform the high voltages comprising the energy to        microwaves.    -   The circulator C is a safety device, which allows the incident        waves to pass and redirects the reflected waves to a water        ballast, where the waves are absorbed, thus raising the water        temperature.    -   The double coupler BC makes it possible to know the reflected        and incident powers by virtue of the milliwattmeter MW.    -   The automatic stub system SA is composed of 4 insertable screws        in the waveguide for the purpose of attenuating the reflected        power of the system.    -   The iris I and the short-circuit piston P make it possible to        adapt the microwave system to the substance to be treated. In        other words, to favor better absorption by the substance of the        power emitted by the generator, the electric field must be        maximal at the location of the solution, which can be achieved        by appropriate adjustment of these two elements.    -   The system is equipped with two cooling systems SR in order to        prevent any overheating.    -   The substance is placed in the applicator AP, formed by        single-mode cavities resonating at the emission frequency along        a beam in the direction of the guide.

The pilot is adapted to the microwave system. It comprises the microwavereactor, positioned in the field of the waveguide. The tests can beperformed under static or dynamic conditions.

II—Results:

The tests were performed by means of a 6-kW magnetron generatoroperating at the frequency of 2450 MHz. The single-mode applicator wasconstructed on the basis of a rectangular waveguide of 86 mm width and43 mm height. In this type of applicator, the distribution of theelectric field is localized and the Pyrex™ reactor is placed in maximuminteraction therewith by virtue of a short-circuit piston. Animpedance-matching device, placed between the generator and theapplicator, also assures the adjustments necessary for optimal transferof energy into the product to be treated.

The tests were performed under static and dynamic conditions.

Two types of chimney members CH were tested on two types of products:

-   -   standard cylindrical chimney members (see FIG. 3)    -   conical chimney members (see FIG. 4)        and    -   water: polar molecule with good dielectric characteristics    -   rapeseed oil: molecule with poor dielectric characteristics

The values of the dielectric characteristics of these products arepresented in the table below:

Relative permittivity ε′ Loss factor ε″ Loss angle tan δ Water 80 200.25 Rapeseed oil 4.5 0.2 0.044

The experiments performed on 1.5 kg of product demonstrate the efficacyof these new chimney members:

Tested Chimney member power Water Rapeseed oil Standard (cylindrical) 2kW no arcs arcs in 10 min Conical (invention) 4 kW no arcs no arcsIII—Tests Performed

All tests were performed with rapeseed oil.

a—Test with Two Standard Chimney Members (Prior Art) of 95 and 65 mmHeights and a Microwave Reactor of 30 mm Diameter.

See FIG. 5

The test was performed on rapeseed oil with a microwave tube having aninside diameter of 30 mm and a height of 1 m.

P reflected Leaks P emitted (kW) (W) (mW/cm²) Remarks 0.5 160 0 to 0.2 1279 0.3 2 600 0.4 Arcs, glass deformed

At the moment when arcs began, the temperature was 240° C. The arcs didno break the glass, but deformed it. The strike occurred just at thebeginning of the upper chimney member.

see FIG. 6

The places of the reactor that are most susceptible to arcs are thosewhere the distance between waveguide and chimney member of the reactoris shortest. See FIG. 7

These arcs are caused by the fact that the electric field is too strong.Attempts were then made to increase the volume of product exposed to thefield.

b—Chance of Configuration

The waveguide was modified in such a way as to expose a larger volume tothe field.

Old Configuration

In the old configuration, the reactor traversed the waveguide at rightangles to the direction of propagation of the waves.

See FIG. 8

See FIGS. 9 and 10

Total length=77.86 cm

Since λg/2=8.66

then 8 (λg/2)=69.28 and

9 (λg2)=77.94

9 half-periods are counted between the iris and the piston

New Configuration

In the new configuration, the reactor traverses the waveguide parallelto the direction of propagation of the waves.

See FIGS. 11 and 12

Total length=63 cm

7 (λg/2)=60.62

8 (λg2)=69.28

Slightly more than 7 half-periods are counted between the iris and thepiston.

The reactor was filled with rapeseed oil and power tests were performed.

At 5 kW, an arc developed in 5 minutes. At 2 kW, it appeared at the endof 36 minutes. In both cases, the temperature attained did not exceedthe desired temperature level.

Once again, a single arc strike occurred at the junction between thechimney member of the reactor and the waveguide:

See FIG. 13

To limit the presence of electric arcs, it must therefore be ensuredthat the reactor is not too close to the waveguide.

The old configuration (vertical arrangement) achieved better results.The next tests were performed with this first configuration but with newshapes of chimney members.

c—Use of Conical Chimney Members

Two criteria must be taken into account:

-   -   1—the volume exposed to the field    -   2—the distance between the reactor and the waveguide constituted        by the chimney member

New chimney members are designed to meet these two criteria. They arecharacterized as conical. More precisely, they comprise a standardcylindrical portion and a conical portion at the level of the waveguide.They replace the straight cylindrical chimney members.

See FIGS. 3 and 4

The microwave reactors can then have different shapes:

See FIGS. 14 and 15

With approximately:V1=4.33*Π*x ²/4V2=9.95*Π*3²/4=70.33 cm²V3+V 4=9.95*Π*(x−3)²/4For x=3 cm, Vtotal=171.2 cm²For x=5 cm, Vtotal=282 cm²For x=6 cm, Vtotal=394.3 cm²

Power tests at 4 kW were performed on reactors of 50 mm (x=5 cm) and 30mm (x=3 cm) diameter.

With the 50-mm reactor, an arc developed at the end of 6 minutes. Thereactor was too close to the waveguide.

In contrast, with the reactor having 30 mm diameter (straight reactor),no arc developed. The only arcs that can occur were observed when thereactor was weakly centered.

d—Ventilation by Humid Air

Additional tests were performed to optimize the results obtained withthese new chimney members a little more.

The tests were performed with the conical chimney members and a straightreactor of 30 mm diameter (better conditions, see II-c).

To remove the static electricity, it is necessary to promote goodventilation by humid air or by another gas having comparable values ofdielectric constants (example: SF6 at 1 bar). In the present case, watervapor was injected at the applicator. To prevent water from condensingon the reactor walls, it was necessary to add suction at the outlet ofthe chimney members.

With gentle suction, an arc developed at 282° C. and Pi=5 kW.

With very strong suction, an arc developed at 284° C. and Pi=6 kW. At 5kW, however, no arc developed.

Ventilating with humid air therefore improves the results. Nevertheless,the ventilation must be sufficiently intensive to achieve a real effect.

Conclusions of the Tests:

The tests performed at 2450 MHz show that the system of chimney membersin “conical” shape then makes it possible to avoid electric arcs at highemitted power (4 kW, instead of 2 kW with the standard chimney members).During operation at such powers, the desired temperature level (up to400° C.) is reached very rapidly, or in other words in less than 15minutes for the treatment of 1 kg of product.

It will be entirely preferable, without being limitative, to use thedimensions and shapes illustrated in FIG. 4, which represents the bestembodiment of the invention to date. As is evident, a chimney memberhaving a conical lower portion and a cylindrical upper portion is usedin this case.

The invention also covers all the embodiments and all the applicationsthat will be directly accessible to the person skilled in the art fromreading this application, from his own knowledge and possibly fromsimple routine tests.

1. An dielectric heating applicator, comprising: a waveguide and lateralchimney members, for dielectric heating of any compound, at microwavefrequencies or high frequencies, under static or dynamic conditions,with relative power density higher than that of the usual applicators,without risk of electric arcs or “discharge”, regardless of thedielectric constants of the said compound, wherein the said applicatoris provided with at least one resonant cavity chimney that extendsaround the waveguide, for treatment of the product.
 2. An applicatoraccording to claim 1, wherein the cavity is formed on each side of thewaveguide.
 3. An applicator according to claim 1, wherein the cavity isformed around the waveguide by one or more chimney members.
 4. Anapplicator according to claim 3, wherein the chimney member or chimneymembers is or are placed on each side of the waveguide, around theresonant cavity.
 5. An application according to claim 1, wherein theshape of the said cavity formed around the waveguide is chosen fromamong: symmetric shapes, and shapes composed of at least a conical base,a spherical shape or a shape of ellipsoidal volume, the broadest portionopening into the waveguide.
 6. An applicator according to claim 3,further comprising: a plurality of chimney members of identicalgeometry.
 7. An applicator according to claim 3, wherein the chimneymembers are composed of two main portions: an upper portion, which mustbe close as possible to the reactor in order to prevent waves fromleaking out, and a lower portion whose shape flares toward the waveguideto prevent electric arcs.
 8. An applicator according to claim 7, whereinthe upper portion of the chimney members must be as close as possible tothe reactor in order to prevent leakage of waves, and it can havecylindrical shapes with circular, rectangular or square cross section.9. An applicator according to claim 8, wherein the chimney members havea geometry composed of different successive shapes.
 10. An applicatoraccording to claim 8, wherein the upper portion of the chimney membershas a cylindrical shape with circular cross section, in order to conformbest to the shape of the reactor and to avoid the presence of edges,which favor electric arcs, the height of this portion of the chimneymember is determined so as to exclude any leakage of waves.
 11. Anapplicator according to claim 8, wherein the lower portion of thesechimney members, or in other words that close to the waveguide, is offlared shape.
 12. An applicator according to claim 11, wherein saidshape is chosen from among the conical and/or spherical shapes havingvariable angles relative to the vertical, and from the pyramidal shapeshaving square or rectangular bases.
 13. An applicator according to claim11, wherein the base diameter of these flared shapes must not exceed thewidth of the waveguide, and then the height and apex angle of the flaredportion are fixed as a function of the power used.
 14. Applicatorsaccording to claim 1, wherein there are used single-mode microwaveapplicators at 2450 MHz, and in that the recommended waveguide width forremaining in TE 0.1 mode (transverse electric) ranges betweenapproximately 70 and 100 mm, the TB 0.1 fundamental mode of excitationpermitting the wave to propagate along a single arc.
 15. Applicatorsaccording to claim 1, wherein there are used applicators operating atother microwave frequencies and at high frequencies.
 16. Applicatorsaccording to claim 1, wherein the chimney members comprise an upperstandard cylindrical portion and a lower conical portion at thewaveguide.
 17. Applicators according to claim 1, wherein there are usedhigh-frequency applicators chosen from among the following: applicatorsof capacitive type, formed from two capacitor foils between which thereis applied the high-frequency voltage of the generator, the saidapplicators being used for heat treatment of materials whose volumecomprises a parallelepiped in which one of the sides is sufficientlythick (>10 mm), rod applicators for flat materials, comprising tubularor rod electrodes, the said applicators being used for heat treatment ofmaterials whose volume comprises a parallelepiped in which one of thesides is not sufficiently thick (<10 mm), applicators for thread-likematerials, formed of loops, microwave applicators, chosen from among:localized-field applicators: single-mode cavity, diffuse-fieldapplicators: multimode cavity, near-field applicators: radiating-antennaguide.
 18. Applicators according to claim 1, wherein a resonantmicrowave system is created by a localized-field or a diffuse-fieldapplicator.
 19. An applicator according to claim 18, wherein saidlocalized-field or a diffuse-field applicator creates a “single-mode”system (localized field), which is formed from single-mode cavitiesresonating at the emission frequency along a beam in the direction ofthe guide.
 20. An applicator according to claim 18, wherein saidlocalized-field or a diffuse-field applicator creates a “multimode”system (diffuse field).
 21. An applicator according to claim 3, whereinthe length of each chimney member is determined so as to exclude anyleakage of waves and to comply with the safety measures relating topersonnel and telecommunications.
 22. Use of the applicators or chimneymembers according to claim 1 for application of microwave orhigh-frequency electromagnetic waves for heating applications oncompounds that absorb the radiation weakly and on compounds having highdielectric constants (ε′>5 and εΔ>0.5).
 23. Applications according toclaim 22 for performing heat treatments on compounds that absorbelectromagnetic waves weakly or on polar or polarized compounds. 24.Applications according to claim 22 for the treatment of fatty acidesters (unsaturated or otherwise), of hydrocarbons (unsaturated orotherwise), of aromatic compounds and of derivatives of the latter, andof products that absorb electromagnetic waves, to increase theproduction capacity of a given system (fatty and non-fatty alcohols,carboxylic acids, amines, etc.), and for all reactions of“lipochemistry”, with in particular a very strong interest for the caseof products that absorb electromagnetic waves weakly, such as forisomerization of fatty acids or of esters of monounsaturated orpolyunsaturated fatty acids, or of waxes, and in particular of castoroil.
 25. Applications according to claim 22, wherein there are achievedall the heating applications involving a single reactant or a mixture ofreactants in variable proportions, such as esterification,transesterification, epoxidation, sulfatization, phosphatization,amidification, polymerization and polycondensation reactions as well asdecolorization, deodorization and the systems for elimination ofvolatile compounds.
 26. Applications according to claim 22 for synthesisof polymers of unsaturated fatty acids, of esters of unsaturated fattyacids, of esters of unsaturated fatty acids, or unsaturated hydrocarbonsor of derivatives of such products by dielectric heating with microwave.27. Applicators according to claim 11 wherein there are used chemicalagents chosen from among the following: the products that absorbelectromagnetic waves weakly or the products that absorb strongly or amixture of the two, with or without additions of catalysts or weakly orstrongly absorbing additives, strongly absorbing products: the fatty ornon-fatty alcohols, fatty or non-fatty amines, carboxylic acids,acetals, ketones, enols, peracids, epoxides and chemical compoundscontaining a polar or polarized function, as alcohols: sorbitol,glycerol, mannitol, glycols, vitamins (such as tocopherol, ascorbicacid, retinol), polyphenols, sterols (including the phytosterols) and asamines: ammonia, primary, secondary and tertiary alkylamines(methylamine, dimethylamine, trimethylamine, diethylamine), the fattyamines (oleic amines, alkylamines of coconut oil), the aminoalcohols,(monoethanolamine MEA, diethanolamine DEA, triethanolamine TEA;3-amino-1,2-propanediol, 1-amino-2-prop anol) and ethoxylated amines(2,2′-aminoethoxyethanol; amino-1-methoxy-3-propane), saturated orunsaturated, straight-chain or branched, catalysts or additives: theacid catalysts such as paratoluenesulfonic acid, sulfuric acid,phosphoric acid, perchloric acid, etc., the basic catalysts such assodium hydroxide, potassium hydroxide, alkali metal and alkaline earthalcoholates, sodium acetate, triethylamines, pyridine derivatives, etc.,the acid and/or basic resins of the Amberlite™, Amberlyst™, Purolite™,DoweX™ and Lewatit™ type, zeolites, enzymes and carbon blacks, weaklyabsorbing products: the animal or vegetable oils and fats and thepolyterpenes, some of which are derived from the said oils and fats,oils or fats of animal origin: sperm oil, dolphin oil, whale oil, sealoil, sardine oil, herring oil, shark oil, cod-liver oil, neatsfoot oiland beef, pork, horsemeat and mutton fats (suets), oils of vegetableorigin: rapeseed oil, sunflower-seed oil, peanut oil, olive oil, walnutoil, corn oil, soybean oil, linseed oil, hemp oil, grape-seed oil,coconut oil, palm oil, cottonseed oil, babassu oil, jojoba oil, sesameoil, castor oil, dehydrated castor oil, hazelnut oil, wheat-germ oil,borage oil, onager oil and tall oil, components of animal or vegetableoils: squalene, extracted from the unsaponifiable fractions of vegetableoils (olive oil, peanut oil, rapeseed oil, corn-germ oil, cottonseedoil, linseed oil, wheat-germ oil, rice-bran oil), or the squalenecontained in shark oil, the said oils and fats of animal or vegetableorigin as well as the derivatives thereof being capable of beingsubjected to a preliminary treatment aimed at making them more reactiveor, on the other hand, less reactive, unsaturated hydrocarbons: analkene, such as a terpenoid hydrocarbon or hydrocarbons, meaning apolymer or polymers of isoprene, or a polymer or polymers of isobutene,styrene, ethylene, butadiene, isoprene or propene, or a copolymer orcopolymers of these alkenes, individually or in mixtures,monounsaturated or polyunsaturated fatty acids or fatty acid esters,waxes, castor oil.
 28. An dielectric heating applicator, comprising: awaveguide and lateral chimney members, for dielectric heating of anycompound, at microwave frequencies or high frequencies, under static ordynamic conditions, at relative power density higher than that of theusual applicators, without risk of electric arcs or “discharge”,regardless of the dielectric constants of the said compound, whereinsaid applicator is provided with at least one chimney member of geometryadapted to form a resonant cavity around the waveguide, for treatment ofthe product under consideration.
 29. Chimney members for energyapplicators for dielectric heating of any compound at microwavefrequencies or high frequencies, under static or dynamic conditions,with high power density, without risk of electric arcs or “discharge”,regardless of the dielectric constants of the said compound, wherein thesaid chimney members are such as described in claim 1.